1. Field of the Invention
The present invention relates to a polymerizable composition particularly used for a tooth treatment.
2. Description of the Conventional Art
The present invention relates to a polymerizable composition used by mixing one or more kinds of liquid and powder. More particularly, the present invention relates to such a polymerizable composition that a liquid composition does not gelate even though the liquid composition before polymerization is stored for a long period of time without being refrigerated, and a curing time does not change with time, that is, the curing time is neither delayed nor quickened by being stored.
A method of combining an organic peroxide and an aromatic tert-amine as a chemical polymerization catalyst has been conventionally used to cure a polymerizable composition at ordinary temperature, where the polymerizable composition includes a monomer, an oligomer, and a prepolymer of acrylate, methacrylate, or the like which have radical polymerization characteristic. In this method, curing time is controlled and preservation stability of the composition before polymerization is increased, by adjusting an amount of the organic peroxide blended with the liquid component and an amount of the aromatic tert-amine blended with the powder component, and also using a polymerization inhibitor together. However, the polymerizable composition has a problem that a cured body after polymerization is discolored while time passes by the aromatic tert-amine. In addition, the organic peroxide is unstable, so that the liquid component easily gelates before polymerization when a great amount of the organic peroxide is blended with a liquid component and the liquid component is stored for a long period. By contrast, when a great amount of the polymerization inhibitor is blended with the liquid component in order to secure long-term preservation stability, the curing time becomes very long. Therefore, the conventional polymerizable composition should be stored in a refrigerator for restraining the reaction of the organic peroxide.
As another chemical polymerization catalyst, a composition in combination of an organic aromatic compound including at least one —SO2— group, a peroxide, and a aromatic tert-amine is used. However, since the organic peroxide and the aromatic tert-amine are used, there are still problems that a cured body discolors and preservation stability is low.
Further, a polymerization method of using trialkylborane is also known. However, trialkylborane has a disadvantage unable to be previously blended with the polymerizable composition including a (met)acrylate compound having radical polymerization characteristic since trialkylborane is oxidized easier than aromatic tert-amine. Therefore, trialkylborane should be stored in a vessel separately from the (meth) acrylate compound, and should be added to the polymerizable composition at each use. Thus, the operation is complicated.
The present inventors developed before a polymerizable composition including a ternary catalyst consisting of a pyrimidinetrione derivative, an organohalogen compound, and an organometallic compound, and applied a patent for this composition as in Japanese Patent Application Laid-Open No. 2003-105008. Since this composition does not include amine, a cured body does not discolor, and the composition can be used under acid conditions. However, the ternary catalyst still has a problem in preservation stability of the pyrimidinetrione derivative.
In addition to this, for example, Japanese Patent Application Laid-Open No. 58-219281 discloses a combination of cumene hydroperoxide and a thiourea derivative. This combination has higher thermal stability than that of conventional composition. However, a composition using the combination has a problem that a curing reaction of cumene hydroperoxide and a thiourea derivative is slow. Even if a blending concentration is sufficient, the composition cannot obtain a polymerization speed which is appropriate for dental adhesives.
In order to improve this composition, for example, Japanese Patent Application Laid-Open No. 2007-056020 discloses a combination of cumene hydroperoxide and acetylthiourea, for a redox reaction in the presence of a copper compound. Since this composition has comparatively high thermal stability and does not include an aromatic tert-aimine, a cured body does not discolor with time after cure. Further, this composition is not influenced by acid substituent of an acidic (meth)acrylate, where the acidic (meth)acrylate compound is conventionally blended in order to give adhesive property to a composition. Thus, the composition has excellent preservation stability. However, when an operator adheres a dental prosthesis to a tooth, a dental material is required particularly to have a property that the material is properly cured within a time desired by an operator, and to be constant in a curing time for every product. About these points, the combination still does not satisfy the requirements of stability of the curing time.